[PATCH] x86_64: Switch to the interrupt stack when running a softirq in local_bh_enable()

This avoids some potential stack overflows with very deep softirq callchains.
i386 does this too.

TOADD CFI annotation

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 31 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index 0696e025dce5..096d470e280f 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -918,3 +918,15 @@ ENTRY(machine_check)
 ENTRY(call_debug)
        zeroentry do_call_debug
 
+ENTRY(call_softirq)
+        movq %gs:pda_irqstackptr,%rax
+        pushq %r15
+        movq %rsp,%r15
+        incl %gs:pda_irqcount
+        cmove %rax,%rsp
+        call __do_softirq
+        movq %r15,%rsp
+        decl %gs:pda_irqcount
+        popq %r15
+        ret
+
diff --git a/arch/x86_64/kernel/irq.c b/arch/x86_64/kernel/irq.c
index cc3fb85f5145..849a20aec7ca 100644
--- a/arch/x86_64/kernel/irq.c
+++ b/arch/x86_64/kernel/irq.c
@@ -135,3 +135,22 @@ void fixup_irqs(cpumask_t map)
         local_irq_disable();
 }
 #endif
+
+extern void call_softirq(void);
+
+asmlinkage void do_softirq(void)
+{
+        __u32 pending;
+        unsigned long flags;
+
+        if (in_interrupt())
+                return;
+
+        local_irq_save(flags);
+        pending = local_softirq_pending();
+        /* Switch to interrupt stack */
+        if (pending)
+                call_softirq();
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL(do_softirq);